As the most general method for obtaining multicolor images, silver salt photography has been widely used up to now from the standpoints of high sensitivity, high image quality and abundance of gradation reproducibility. However, the silver salt photography has a defect that the image forming process is tedious since it comprises the steps of imagewise exposure, processing with a developer, and conversion of the remaining silver halide into a silver complex soluble in water or a silver salt stable to light.
For the purpose of obviating this defect, dry processable silver salt photographic materials are disclosed in Japanese Patent Publication (OPI) No. 48764/'84 (the term "OPI" as used herein means an "unexamined published Japanese patent application") and so on; dye diffusion transfer process photographic light-sensitive materials in British Patent No. 249530, U.S. Pat. Nos. 2,020,775, 2,004,625, 2,217,544, 2,255,463 and 2,699,394, and so on; silver dye bleach process photographic light-sensitive materials in U.S. Pat. No. 2,844,574, and so on.
On the other hand, recording methods using no silver salt in a recording material, but allotting the mechanism of multicolor recording to a recording apparatus, e.g., electrophotography, a thermal transfer method, an ink-jet method, etc., have been employed. However, these methods suffer from disadvantages that they require a large-sized apparatus and lack reliability of the obtained records, it takes much time to renew consumables, and so on.
Nonsilver salt recording materials into which multicolor recording mechanisms, which can work in combination with, e.g., a pressure-sensitive, heat-sensitive or light-sensitive color-producing method, are incorporated are disclosed, e.g., in Japanese Patent Publication (OPI) Nos. 134282/'88, 154386/'88, 172680/'88, 172681/'88, 189282/'88, 218392/'88 and 45084/'88 and so on.
As an example of conventional color-producing mechanisms incorporated in heat-sensitive recording materials, mention may be made of the mechanism in which plural color-producing units sequentially undergo color-producing reaction with an increase in thermal energy applied thereto, and the colors produced are simply mixed to cause changes in hue while accompanying turbidity, as disclosed in Japanese Patent Publication Nos. 19989/'76, 11231/'77, Japanese Patent Publication (OPI) Nos. 88135/'78, 133991/'79, 133992/'79, etc. As another example, mention may be made of the mechanism in which a decolorizing mechanism, such that color production in the color-producing unit having a higher thermal response temperature and the action of a decolorizer take place at the same time to decolorize the color produced in the color-producing unit having a lower thermal response temperature, is incorporated, as disclosed in Japanese Patent Publication Nos. 17868/'75, 5791/'76, 14318/'82, 14319/'82, and Japanese Patent Publication (OPI) No. 161688/'80.
In the recording materials having plural recording layers in a multilayer form to get a multicolor recording mechanisms, as described above, it is important to prevent the undersirable migration of ingredients of each layer to other layers.
More specifically, light-sensitive or/and heat-sensitive recording materials which utilize a combination of the first layer comprising a basic dye and a color developer with the second layer comprising a diazo compound and a coupler have problems that the color developer contained in the first layer acts on the second layer to accelerate the coupling reaction therein, and thereby fog generation goes on with the lapse of time in the second layer, and basic substances generally contained as a coupling accelerator in the diazo compound-coupler system hinder the color-producing reaction in the first layer to lower the density of the color to be produced in the first layer.